Shama-il Tirmidhi Chapter 39, Hadith Number 1 (248).
Mughirah bin Shu’bah Radiyallahu ‘Anhu reports that Rasuluilah Sallallahu ‘Alayhi Wasallam performed such lengthy nafl prayers, that his mubaarak legs became swollen. The Sahaabah said : “You undergo such great difficulties, where Allah had forgiven your past and the future…